Currently, images can be displayed sheets of paper carrying permanent inks or displayed on electronically modulated surfaces such as cathode ray displays or liquid crystal displays. Sheet materials can carry magnetically written areas carrying ticketing or financial information, however magnetically written data is not visible.
For an example of electronically writable displays, see PCT/WO 97/04398, entitled "electronic Book With Multiple Page Displays." This reference discloses the assembling of multiple electronically written display sheets into a "book", each sheet provided with means to individually address each page. The disclosure sets forth prior art in forming thin, electronically written pages, including flexible sheets, image modulating material formed from a bi-stable liquid crystal system, and thin metallic conductor lines on each page. The device described requires ". . . transparent conducting polymers . . . " formed over the light modulating material. Formation of transparent conductors of the required conductivity require complex vacuum sputtering and photo-lithographic processes.
Fabrication of flexible, electronically written display sheets is disclosed in U.S. Pat. No. 4,435,047. A first sheet has transparent ITO conductive areas and a second sheet has electrically conductive inks printed on display areas. The sheets can be glass, but in practice have been formed of Mylar polyester. A dispersion of liquid crystal material in a binder is coated on the first sheet, and the second sheet is pressed onto the liquid crystal material. Electrical potential applied to opposing conductive areas operates on the liquid crystal material to expose display areas. The display ceases to present an image when de-energized. The Taliq Company supplied products formed using the two sheet method. Offsetting the two sheets permitted connection to conductive traces on the two sheets.
The prior art typically requires multiple, separate layers to build up the display. The electrical traces and transparent conductive layers are typically formed through repeated vacuum deposition and photolithography of materials on the substrate. These processes are expensive and require long processing times on capital intensive equipment.
The prior art discloses isolating each conductor on separate sides of the display, and connecting the traces to drive electronics using solder connections, wire bonds or pressure contact. Such connections do require that both sets of traces be exposed on a surface for the connection process. The uniform, multi-layer structure prevents connection to the inner conductive layer.
A problem with the prior art is that layers that should not be distinguished frequently are distinguishable and can be seen by a viewer thereby degrading the quality of the viewed image.